Method of and means for transmitting signals



9 1927. Aug J. w. HORTON METHQD 0F AND MEANS FOR {TRANSMITTING SIGNALS Filed Dec. 15. 192

m m V wzx/ Patented rig; 9,1927. I

osnrn WARREN Honron, or EAST on, new messy, ASSIGNOB no WESTE ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, ,N. Y., A CORPO'I'ION OF NEW YORK.

mnrrron or AND mnens r03 sm'rrme ere-areas.

Application filed December 13,1920. Serial no. 430,143.

This invention relates to a carrier current system and more particularly to an arrangement whereby the amplitudes of the carrier and side-band .current components suppliedv 5 to the line by a modulating tube may be regulated.

In a system using a carrier current of frequency within the voice range modulated by a current of the usual ringing frequency, the

n amplitude of the carrier'current in the modulator output circuit will exceed that of the side-bands. If the output current of a modulator is impressed upon a resonant cir- "cuit tuned to the frequency of one of theside-bands, the impedances offered to the carrier current would be reater than that offered to the selected si e-band and the amplitude of the current of side-band frequency would exceed that of the carrier.

In such a system, wherein a signal is transmitted, through voice range repeaters, the line current capable of developing a fixed amount of energy of the original frequency when demodulated in any given cir- '20 cuit'will be a minimum when the side-band and carrier current components are of equal amplitude, hence it will be obvious that under either of the conditions stated above, the

maximum signaling effect will not be obtained 'at the distant receiving station.

' The primary object of this invention is to provide an arrangement in a system of this type whereby a maximumsignaling current may be transmitted to the receiving station under the above-mentioned conditions for line current and power.

Another object is to control the ratio. of the amplitudes of the carrier and side-band current components supplied by the output A further object is to equalize the amplitude's of the carrier and side-band current components transmitted to the-line. These objects and others which will ap- 40 circuit of a modulating tube.

pear as. the nature of the invention asset.

forth may be accomplished by associating withthe outputcircuit of a modulating tube, a resonant circuit having means to vary lts relativeimpedance to the current componame of carrier and side-band frequencies. The ratio of'these impedances depends upon the frequency relation of the two currents and the resonant.characteristics of the circuit, hence with given frequencies for quency of the these currents, the impedances-ofi'ered to the two frequencies in question may be made inversely proportional to their amplitudes, by varying the damping of the resonant circuit. i In the arrangement herein shown an adustable resistanceis connected in a tuned .circuit associated with the modulator output circuit for this purpose, and by a proper adJUStIIIGIIt of this resistance, equalization of the amplitudes of the current components of carrier and side-band frequencies, under the conditions hereinbefore mentioned as to power and line current, may be secured.

For a complete understanding of the invention reference will now be made to the following specification and attached drawmg in which, Fig. 1 shows one-form of the invention and Fig. 2 an alternative method I for connecting the output circuit of the modulator to the input circuit of the amplifier in an arrangement of the type shown in lue means for supplying a carrier current is herein shown as consisting of a vacuum tube oscillator, though any other form of generator adapted to supply acurrent of carrier frequency may be used.

As is Well known an oscillator of this type comprises a hot filament or cathode, a grid or impedance control element' 2, and

an anode or plate 3, enclosed in an evacu-- ated yessel 4, havin an input circuit connected between the %lament and 'gridfand an output circuit including the filament and a pla a coupling connecting these two circuits so that increments of energy are derived f cm the output circuit and fed back to the nput circuitto controlthe flow of curr nt in the former circuit, and an oscillatory circuit associated with the feed-back connector to determine and control the freoscillations produced by the generator. la v As herein illustrated, the input circuit may be traced from-the filament 1, through the winding 5 shunted by an adjustable con- .denser 7 and the. battery 8, t othe grid 2. The output circu'itincludes; {thefilament 1,

plate 3, condenser 9, coil 6, and a resistance 11. The condenser 9 serves as a low impedance path for the high frequency oscil-f lations produced in the output circuit, while preventing direct current flow thereto from Y .said source through the plate circuit.

the source of plate current. A choke coil 10 Connected in the plate supply circuit prevents the flow of oscillatory .current through the plate current source, while permitting uni-directional current to flow from In this case the coils and 6 are inductively related to constitute the feed-back couplmg and the coil 5 with the associated condenser 7 constitutes a tuned circuit, the natural 1 period of which may be varied to control v and a polarizing battery 19 for the grid 14.-

the frequency -of the oscillations supplied by the plate circuit'which, as stated above,

A" source of signaling current, herein conventionally indicated as a vibratory current source 20, but which would preferably be the usual plant supply, is connected to a winding 21' which is inductively associated with the coil 17 to supply alternating current of the usual ringing frequency to the input circuit of the modulating tube. 'The tuned circuit 1718 is resonant to-the ringi'ng frequency.

The output circuit of the modulator includes filament 13, plate 15, a condenser 21, anda tuned circuit comprising an inductance 22 shunted by an adjustable condenser V v23. This circuit is tuned to the side-band selected for. transmission, but such tuning should'be sufliciently broad to permit the flow of some current of carrier frequency while suppressing these condltions owing to the large ampl the, other side-band. Under tude of the carrier current component relatively to that of the selected side-band frequency, the amplitude 'of the current component of carrier frequency present in this .circuit will exceed that of the side-band to be transmitted. y

The condenser 21 operates to exclude unidirectional space current from the oscillatory circuit 2223, while permitting the flow of high frequency currentthereto. A choke coil 24 serves as a low impedance path for direct. current supplied by the source of plate potential, to be referred to oscillatory current more specifically later, while confinin the to the plate circuit of the modulator.

Inductively related to the inductance 22 is a winding 24 consisting of a few turns which is included in a resonant circuit tuned to the selected side band. In addition to the windmg 24, the resonant circuit includes an inductance 25, a resistance .27, and an adjustable condenser 26 connected in shunt to the winding 24, inductance 25 and resistance 27.

Modulated current is transmitted to the resonant circuit by the coupling connection between the windings 22 and 24. The resistance 27 is provided with a sliding contact 28 whereby the amount of the resistance included in the resonant circuit may be regulated.

The frequency relation of the carrier and signaling currents being fixed, the ratio of the impedances offered to the current components of carrier and side-band frequencies flowing through the last-mentioned tuned circuit willdepend upon the resonant characteristics of said circuit. By varying the position of the sliding contact 28, the amount of the resistance 27 included in this circuit'may be regulated, hence the relative impedances offered to currents of these two frequencies may be made inversely propor tional to the impressed amplitudes.

It will therefore be evident that by adjusting the contact 28 to include a pro er amount of the resistance 27, the amplitu es of the current components of the two frequencies in question may be made equal.

Should amplification of the current components to be supplied to the transmission circuit be desirable, the resonant circuit 24 2526- -27 will be included in the input cir cult of an amplifier 32, which extends from the filament 28' to the grid 30. vA olarizing battery 29 for the grid 30 may e connected in the input circuit of the amplifier.

The alternating current output circuit of the amplifier, which includes the filament 28, plate 31, and the condenser 33 is connected to the toll line L whichincludes voicerange repeaters VB. The condenser 33constitutes a low impedance path for the amplified current, but imposes an infinite impedance to the flow of unidirectional current from the plate source to the line. A choke coil 34 is provided to prevent the flow of Ill amplified. current through the plate current source, while permitting the fiow ofcurrent from. said source through the plate circuit and space path within the amplifier.

Plate current is supplied to the several vacuum tube devices by the battery 35 and heating current to their filament by a battery 36, through an adjustable resistance 37. The source of plate currentis connected to the vacuum tube devices throughthe' respective choke coils associated with them.

Selection of the desi-red side band may be attained solely by the tuned circuit 24-25- 26 and 27.

In this. case, as shown .inFig. 2, wherein are used the same reference characters, pro

' .vided with subscripts, as were applied to the same elements in Fig. 1, the output circuit of the modulating tube includes the condenser 21 and the inductance 22,. The condenser 21 performs the same functions as the condenser 21 of Fig. 1.

The circuit 24,25,26 and 27 associated with the inductance 22 is tuned to the side band which is to be transmitted to the line. This circuit, therefore, performs the doublefunction of selecting the desired side band and, by a proper adjustment of the resistance 27 equalizing the amplitudes of the current components of carrier and side-band frequencies supplied tothe load circuit. In

every other respect the circuit arrangement and connections are the same as shown in Fig. 1.

While in the preceding description an oscillator including a space discharge device having a tuned circuit included in its input circuit has been described as a source ofcarj riercurrent, by way of example, it will be appreciated that an oscillator having a condenser shunting the coupling coils to constitute a tuned circuit, as disclosed in U. S. Patent No. 1,356,763, issued October 26, 1920, to Hartley, or a resonant circuit in the output-circuit of the tube, as shown in Fig. 3C on page 69 of the Proceedings of the Institute of Radio Engineers, vol. 6, N0. .2, April, 1918, would be equally effective and may therefore be substituted for the oscillator described above.

Again, while the connection between the output circuit of the modulator and the selective circuit connected to the amplifier is shown as consisting of a coil having a small number. of turns, this .isdone merely with the object of indicatin that these circuits should be loosely coup ed together; hence, any method of effecting a loose coupling between these circuits may be used. Y

' Finally, it may be stated, hat-while for the sake of a complete and clear disclosure, elements of a particular type and one use to which this invention may be applied have been shown and described specifically, itiis'to be understood that this invention is not to be confined to the specific elements illustrated. or the use described, but isto be limited only by the scope. of the appended claims What is claimed is: .1. The method of transmitting signals,

which comprises modulating a carrier cur-.

rent by signaling current and equalizing the amplitudes of the current components, carrier and side-band frequencles trans? mitted whereby maximum signaling effect may be produced at a receiving station.

2. Themethod of transmitting signals, which comprises. modulating a carrier current of audio frequency by current of ringing frequency and equalizing the amplitudes v of the current components of carrier and side band and equalizing the current com-- ponents of carrier and side-band frequencies.

5. In a signal transmitting system, a modu- 'lator, means for impressing carrier current and signaling current on said modulator,

and means in the outgoing circuit from said modulator for selectin one side-band and for varying the impedence to the flow of current components of carrier and side-band frequencies from the modulator in the inverse ratio of their amplitudes.

6. In a signal transmitting system, a modulator, means for impressing carrier current and signaling current on said modulator, and means in the outgoing circuit from said modulator for changing the amplitudes of the current components of carrier and side-band frequencies from said modulator to equal values. I

7. A.- signaling system comprising a source of carrier current, a source of signaling current, a modulator having its input circuit connected to said sources, and a tuned circuit associated with its out ut circuit to se-- lect one side-band, provide with-means to vary the impedance to the flow of current components of carrier and side-band frequenr cies in the inverse ratio of their amplitudes. .8. A signallng system comprlsmg a source of carrier current, a source of current of ringing frequency, a modulator having its input circuit connected to said sources, a tuned circuit selective of one side-band, associated with the modulator output circuit, adapted to equalize the amplitudes of the current componentsof carrier and side-band frequencies.

9. A signaling system comprising a source of carrier current of audio frequency, a"

source of current of ringing frequency, a

modulator having its input circuit connected to said sources, a circuittuned to one sideband associated with theniodulato'r output circuit, and means for changing to-equal values the amplitudes-of. the current conitransmitted whereby maximum signaling effect may be produced at a receiving station.

ponents of carrierand side-band frequencies 10. The method of transmitting signals over a toll line provided with voice range repeaters, which comprises modulating a carrier current of audio frequency by current a maximum signaling effect at a receiving station. 7 a p v 11. A signal transmitting system compris- 'ing a toll line including voice range repeaters, means for modulating a carrier current of audio frequency by current of ring- .ing frequency,and means for equalizing the amplitudes of the current components of carrier and side-band frequencies transmitted over said liue whereby minimum line current will produce a maximum signaling effect at the receiving station. I

12. A signaling system comprising a source of carr er current, a-source of signaling current, a ,modulator having its input c cult connected to said sources, a selectlng circuit connected to the modulator output circuit for selecting one side-band, and means included in said selecting circuit to adjust the amplitudes of the transmitted side-band with respect to the amplitude of the transmitted unmodulatcd carrier current.

13. A signalii'ig system comprising a source of carrier current, a source of signaling. current, a modulator-having its input circuit connected to said sources, a tuned circuit connected to the modulator output circuit to select one side-hand and means included in said tuned circuit to adjust the 1 amplitudes of the transmitted unmodulated my name this 8th day of December, A. D.,

1920. J. WARREN HORTON. 

